Surface subsidence control theory and application to backfill coal mining technology

Solid backfill technology, which can achieve precise control of surface subsidence, has become the primary method used to extract "under three" coal resources (under railways, buildings, and water bodies), especially under buildings. This paper proposes a probability integration model for surface subsidence prediction based on the equivalent mining height (EMH) theory and describes the basic control principle for surface subsidence, i.e., guaranteeing a maximum security standard for surface buildings, based on the maximum EMH, by controlling the backfill body's compression ratio (BBCR). Based on this control principle, an engineering design process for solid backfill mining under buildings was established, and an engineering design method that employs the BBCR as the critical control indicator and a method for determining the key parameters in subsidence prediction are proposed. In applications at the Huayuan coal mine in China, the measured subsidence values were less than predicted; the measured BBCR was controlled at a level higher than 90 %, which was greater than in the theoretical design; the surface subsidence of buildings was controlled at mining level I. The results of application of the methods proposed in this paper show that the basic principles of controlling the BBCR and maximum EMH provide clear guidance for surface subsidence control in solid backfill mining engineering practice.